The present invention concerns a WORM (Write Once Read Many) type optical disk driver, particularly a circuit for inhibiting overwriting of data on the recording regions of a disk.
Generally, the data once written on a WORM type optical disk should not be erased or destroyed under any circumstances, so that it can be almost permanently retrieved. On the WORM type disk is formed spirally or concentrically a track, which is pitted by using a laser to write desired data. In retrieving the data, a laser beam tracks precisely the pits formed on the disk. The laser beam for writing has much higher power than the laser beam for reading.
Conventionally, when tracking the disk many factors including, circuit unstability of the WORM type optical disk driver, external impacts, flaws on the disk, dusts, etc., may cause the write laser beam to be emitted upon the track portions previously storing data, thus destroying the previously stored data.